oracle delete millions of rows without any rollback

If you have a table with millions of rows and you want to delete e.g. 100’000 of them, all changes will be noticed in your rollback segment. So it can be, that one ‘delete’ – this means one transaction! – cannot be hold in your rollback segment. The result is a broken job and ORACLE feedback in an ORA error message. To resolve this, a small PL/SQL procedure with dynamic SQL is generated.

Solution:

To make a good demonstration I create a table big_emp derived from SCOTT.EMP

create table big_emp as select * from emp.

Execute several times insert into big_emp select * from big_emp; gives me a table with 1’114’112 rows.

=> only 11 distinct rows exists

Create PL/SQL procedure:

CREATE OR REPLACE PROCEDURE delete_tab (tablename IN VARCHAR2,

empno IN NUMBER ,

nrows IN NUMBER ) IS

sSQL1 VARCHAR2(2000);

sSQL2 VARCHAR2(2000);

nCount NUMBER;

BEGIN

nCount := 0;

sSQL1:=’delete from ‘|| tablename ||

‘ where ROWNUM < ‘ || nrows || ‘ and empno=’ || empno;

sSQL2:=’select count(ROWID) from ‘ || tablename ||

‘ where empno= ‘ || empno;

LOOP

EXECUTE IMMEDIATE sSQL1;

EXECUTE IMMEDIATE sSQL2 INTO nCount;

DBMS_OUTPUT.PUT_LINE(‘Existing records: ‘ || to_char(ncount) );

commit;

EXIT WHEN nCount = 0;

END LOOP;

END delete_tab;

/

Execute above created procedure

SQL> execute delete_tab(‘big_emp’,7369,5000)

Existing records: 60537

Existing records: 55538

Existing records: 50539

Existing records: 45540

Existing records: 40541

Existing records: 35542

Existing records: 30543

Existing records: 25544

Existing records: 20545

Existing records: 15546

Existing records: 10547

Existing records: 5548

Existing records: 549

Existing records: 0

PL/SQL procedure successfully completed.

Conclusion:

Normally deleting just one employee from big_emp generates more than 10-Megabyte Rollback for ca. 100’000 deleted rows. In opposite of e.g. half of additional rollback using delete_tab function. With this function you adjust the size of rollback segments created by a ‘delete’ statement. Another advantage is, that not one rollback segment is used. After a commit the next rollback segment will fit the next transaction, so the load is distributed about all rollback segments.